JP4394575B2 - Method for forming aramid paper laminate - Google Patents

Description

  The present invention relates to a method for forming an improved laminate comprising an aramid paper and a polymer layer, preferably a laminate comprising two aramid papers separated by a polymer layer.

  Patent Document 1 discloses a method for forming a laminate sheet made of m-aramid paper and a polyester film, in which the formed laminate is calendered and rapidly cooled.

  Patent Document 2 discloses a metal layer bonded to a nonwoven fabric obtained by compressing and bonding a blend of different types of staple fibers together with a matrix of a film-forming polymer-polymer binder.

  Hendren et al., US Pat. No. 6,057,049, discloses a laminate for a honeycomb structure formed from a core comprising poly (m-phenylene isophthalamide) fibrid and a floc and fibrid outer layer of poly (m-phenylene isophthalamide). It is disclosed.

  Otsuka et al., US Pat. No. 5,677, 199 discloses a method for forming a laminate substrate composed of a nonwoven fabric of aromatic polyamide fibers formed by bonding para-aramid and meta-aramid fibers with a resin binder.

JP-A-8-99389 British Patent 1,486,372 US Pat. No. 5,320,892 US Pat. No. 5,948,543

  Aramid sheets or laminates made of paper and polymer layers are useful for transformer applications, where the laminate functions as a dielectric insulator. It would be desirable to improve the internal adhesion of laminates, or the tear strength or elongation at break properties of such laminates.

The present invention is a method for forming a laminate comprising an aramid paper layer, a polymer layer and an aramid paper layer in order,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
b) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
c) polymer is deposited on the more porous side surface of the aramid paper obtained in step a), and d) the aramid paper obtained in step b) is polymerized on its more porous side surface. It relates to a method comprising contacting and laminating to a polymer.

Another embodiment of the present invention is a method of forming a laminate comprising an aramid paper layer and a polymer layer in this order,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is made more porous than the opposite surface exposed to the hot roll temperature ,
b) relates to a method comprising depositing a polymer on the more porous side surface of calendered aramid paper.

  Another embodiment of the invention relates to a method of forming a laminate in which the temperatures of the two calender rolls differ by at least 50 ° C, preferably by at least 100 ° C.

  The starting material of the present invention is aramid paper. As used herein, the term paper is used in its ordinary sense and can be manufactured with conventional papermaking methods and equipment. Aramid fiber material, ie fibrids and short fibers, can be mixed into a slurry and the mixture can be converted to paper, such as with a Ford linear machine or hand-made mold with a forming screen. For methods of forming paper from aramid fibers, see Gross US Pat. No. 3,756,908 and Hesler et al. US Pat. No. 5,026,456. it can.

  The thickness of the aramid paper is not critical and depends on the end use of the laminate and the number of aramid layers used in the final laminate. In the present invention, two layers are used, i.e. one aramid layer and one polymer layer, preferably three layers, i.e. two aramid paper layers and one polymer layer, but may be present in the final product or others. It is clear that there is no upper limit to the number of materials. For purposes of illustration, a five-layer laminate having a first aramid paper layer, a first polymer layer, an intermediate layer made of paper or a second polymer, a third polymer layer, and a second aramid paper layer. Can be formed. The aramid layer, intermediate layer and polymer layer can be composed of different compositions.

  As used herein, the term aramid refers to a polyamide in which at least 85% of the amide (—CONH—) bonds are directly bonded to two aromatic rings. Additives can be used with aramids, other polymer materials can be blended to aramids by weight up to 10%, or copolymers where aramid diamines are replaced with other diamines to 10 percent, or Copolymers in which the aramid diacid chloride is replaced with other diacid chlorides up to 10 percent can be used. In practicing the present invention, the most commonly used aramids are poly (paraphenylene terephthalamide) and poly (metaphenylene isophthalamide), preferably poly (metaphenylene isophthalamide).

  Aramid paper can be calendered between two heated calendar rolls, and the bond strength of the paper is increased by the high temperature and high pressure received from the roll. It is believed that calendering aramid paper in this way also reduces the porosity of the paper, resulting in a decrease in the adhesion of the paper to the polymer layer in the laminate. Good adhesion to the layer is important in an electrically insulating laminate in that it avoids peeling during use. The present invention solves such adhesion problems in aramid paper by using a calendering method in which the porosity of both sides of the aramid paper is different. In one example of the laminate formation of the present invention, two sheets of aramid paper are first calendered and then laminated using an inner polymer layer. Since the surface of the paper has a certain porosity, the type of polymer layer is not considered important in the present invention. Although both thermoplastic and thermosetting polymers can be used, thermoplastic polymers that exhibit a certain fluidity at high temperatures during lamination are preferred. The thermoplastic polymer can also be used in laminating because it can be applied in liquid form to the surface of the aramid paper during or before laminating. However, a layer pre-formed with a thermoplastic or thermosetting polymer may be used. The preformed layer generally has a memory since formation that negatively affects the mechanical properties of the laminate, and therefore the use of liquid polymers is preferred.

  In the present invention, examples of a preferable polymer applied to aramid paper include polyester, and polyethylene terephthalate (PET) is particularly preferable. The PET used may contain various comonomers such as diethylene glycol, cyclohexanedimethanol, poly (ethylene glycol), glutaric acid, azelaic acid, sebacic acid and isophthalic acid. In addition to these comonomers, branching agents such as trimesic acid, pyromellitic acid, trimethylolpropane and trimethylolethane, and pentaerythritol may be used. PET can be obtained from terephthalic acid or its lower alkyl ester (eg dimethyl terephthalate) and ethylene glycol or blends or mixtures thereof by known polymerization techniques.

  General polymers that can be used in the present invention are listed as follows: polyethylene naphthalate, polybutylene terephthalate, polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyethersulfone, polyimide, polyetherimide and aromatic Liquid crystalline polyesters or any mixture or blend thereof may be mentioned.

  It is also understood that in calendering aramid paper, the pressure on the paper of the calendar roll is not critical. When the roll pressure is increased, generally a denser product as a whole is obtained. The degree of density desired depends on the choice of aramid and the final use of the final laminate.

  However, it is important in the present invention to maintain the two calender rolls at different temperatures for the aramid paper forming the laminate. As used in the present invention, calendering paper between two rolls means that the paper is produced in a single calendering with rolls heated to different temperatures, or first of the sheet. It is understood to mean calendering one surface at one temperature and then calendering the opposite surface at a second temperature. Such a temperature difference directly becomes a difference in porosity between both sides of the aramid paper. In order to obtain the advantages of the present invention, a temperature difference of at least 20 ° C. is required. A more preferred temperature difference will be at least 50 ° C and in many cases will be at least 100 ° C.

  The temperature of the two rolls will depend on the aramid used to form the final laminate. In many cases, the same aramid is used to form both outer surfaces of the laminate, but different aramids can be used on both outer surfaces. The choice of aramid will depend on the end use of the laminate. For illustrative purposes, it is clear that the properties of the laminate surface will determine the temperature and temperature difference of the paper calendering process. If a more precise outer surface of aramid paper is required, the temperature of the roll in contact with the surface in calendering may be increased. It will be appreciated that the temperature of the heated roll can be less than the glass transition temperature of the aramid component of the paper. However, in a preferred form, at least one of the heated rolls will be above the glass transition temperature of aramid.

  In the following examples, all parts and percentages are by weight and degrees are in degrees Celsius unless otherwise noted. Initial tear resistance was determined by elongation at break according to ASTM D1004. The tear resistance was determined by the average tear load according to ASTM D1938. In the following examples, the destruction mechanism was determined by investigating and observing how the sample was broken by the above test method.

Example 1
This example illustrates the method of making the laminated calendered aramid paper of the present invention as compared to prior art laminates, and these improved papers provide adhesion to polyester polymer paper. Show the effect.

  In order to show the effect of paper calendering conditions on the final laminate of the present invention, four laminates were made. Aramid paper containing 45% poly (m-phenyleneisophthalamide) floc and 55% poly (m-phenyleneisophthalamide) fibrid was produced using conventional Fordrinier papermaking methods and equipment. The paper was then calendered at 800 pli with two rolls operated at four different temperatures to produce four different calendered papers for lamination.

  The paper A is subjected to temperature difference calendering with two rolls, one roll operated at a surface temperature of 360 ° C. and the other roll at a surface temperature of 300 ° C., and one has a high porosity (low temperature) A temperature difference calendered aramid paper having two different surfaces (by contacting one roll) and the other having low porosity (by contacting a hot roll) was made.

  Paper B is subjected to temperature difference calendering with two rolls, one roll operated at a surface temperature of 360 ° C. and the other roll at a surface temperature of 250 ° C., one having high porosity and the other Produced a temperature difference calendered aramid paper having two different surfaces with low porosity. The paper C is subjected to temperature difference calendering with two rolls, one roll operated at a surface temperature of 360 ° C. and the other roll at a surface temperature of 200 ° C., one having high porosity, Produced a temperature difference calendered aramid paper having two different surfaces with low porosity. Paper D was calendered by two rolls operated at the same surface temperature of 360 ° C. to produce calendered aramid paper having essentially the same surface and essentially the same porosity.

  Using a hot press operating at 288 ° C., a poly (ethylene terephthalate) polyester polymer having an intrinsic viscosity of 0.60 dl / g is sandwiched between two sheets of calendered paper A, B, C and D, respectively Laminated with. For papers A, B, and C that had been subjected to temperature difference calendering, a laminate was produced such that the polymer was in contact with the surface of the calendered paper on the higher porosity side. This three-layer laminate was pressed for 5 minutes and then cooled. The resulting polymer layer was 0.01 inches thick. There was no chemical, flame, heat or corona treatment or similar activation on the paper surface. Examination of laminates containing papers A, B, and C revealed that the polymer melted and flowed between the calendered papers, and testing showed that these laminates had acceptable adhesion. It was. These laminates caused cohesive failure, i.e. failure where the fracture surface was present inside the aramid paper. Examination of laminates containing paper D revealed that the polymer melted and flowed between the calendered papers, and testing showed that these laminates did not have acceptable adhesion. This laminate caused an adhesive failure, i.e. a failure where a fracture surface exists between the aramid paper and the polymer layer.

Example 2
This example shows the effect of the intrinsic viscosity of the extruded polymer on the final properties of the laminate.

  The laminate according to the present invention was produced in the same manner as in Example 1 using the four calendered papers produced in Example 1, but the polymer was a molten poly (ethylene terephthalate) (PET) polyester polymer. Between the two sheets of paper, the polymer is extruded so that it contacts the surface of the more porous paper, and the polymer is PET with an intrinsic viscosity of 0.65 dl / g or 0.80 dl / g. there were. All of the resulting laminates had a polymer layer 0.005 inches thick. Examination of a laminate comprising paper D (prior art) and PET having an intrinsic viscosity of 0.65 dl / g revealed that the laminate failed unacceptably to adhesive failure, i.e., between the paper and the polyester polymer with a slight force. It turns out that it causes. Examination of temperature difference calendered paper A and laminates made with the same polymer revealed that it had acceptable adhesion that caused adhesive failure only after a moderate force was applied. Examination of laminates made from temperature difference calendered papers A, B and C and a PET polymer with an intrinsic viscosity of 0.80 dl / g revealed that the high viscosity polymer affects the failure mode of the laminate. Specifically, laminates made with temperature difference calendered paper A calendered with the smallest temperature difference showed unacceptable adhesion and caused adhesive failure between polymer and paper with only a slight force. Laminates made with temperature difference calendered paper C calendered with the largest temperature difference showed acceptable adhesion and caused cohesive failure, ie failure in the plane of aramid paper. The laminate produced with the temperature difference calendered paper B calendered at an intermediate temperature difference had acceptable adhesion and caused breakage in an acceptable form although cohesive failure and cohesive failure were side by side.

Example 3
This example illustrates one embodiment of the present invention. As was done in Example 2, a polyethylene terephthalate polyester polymer was extruded between two temperature-difference calendered sheets to produce a laminate, but the polymer had an intrinsic viscosity between two aramid papers. The polymer layers were extruded to form different polymer layers. Specifically, the polymer layer is made up of a PET polymer layer having an intrinsic viscosity of 0.65 dl / g, a PET polymer layer having an intrinsic viscosity of 0.80 dl / g, and a PET having a second intrinsic viscosity of 0.65 dl / g. A three-layer structure of polymer layers was formed. The two outer layers of 0.65 dl / g polymer were each 15% of the total thickness of the polymer layer and the 0.80 dl / g polymer was 70% of the total thickness. Two laminates were produced using the temperature difference calendered paper C calendered with the largest temperature difference. A first laminate was made using a PET polymer with an intrinsic viscosity of 0.65 dl / g, and then a second laminate was made using the three polymer layers. The total polymer layer thickness in each laminate was 0.005 inches. Examination of these laminates revealed that they had similar performance, showed acceptable adhesion, and caused cohesive failure, ie failure in the plane of aramid paper. An attempt was made to produce a similar three polymer layer laminate using conventional paper D from the prior art, but the molten polymer did not adhere to conventional paper D and an acceptable laminate was not produced.

Claims (19)

Aramid paper layer,
A method of forming a laminate comprising a polymer layer and an aramid paper layer in order,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
b) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
c) attaching the polymer to the surface of the more porous side of the aramid paper obtained in step a), and
d ) A process comprising laminating the aramid paper obtained in step b) to the polymer with the more porous side surface in contact with the polymer.   The method according to claim 1, wherein the aramid paper obtained in step a) and step b) is the same.   The method according to claim 1, wherein the aramid paper obtained in step a) and step b) is different.   The method of claim 1 wherein a molten polymer is used for polymer attachment in step c).   The method of claim 1, wherein at least one of the papers of step a) and step b) comprises poly (m-phenylene isophthalamide). The method of claim 1, wherein the polymer of step c) comprises polyethylene terephthalate or a copolymer thereof.   The process according to claim 1, wherein the temperature difference of at least one of a) and b) is at least 50 ° C.   The method according to claim 1, wherein the temperature difference of at least one of a) and b) is at least 100 ° C.   The method according to claim 1, wherein at least one of the rolls in a) or b) exceeds the glass transition temperature of aramid. Aramid paper layer,
A method of forming a laminate comprising a polymer layer and an aramid paper layer in order,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
b) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
c) depositing a polymer on each surface of the more porous side of the aramid paper obtained in step a) and step b ), and d) laminating the two papers and the polymer together. Method. Polymer The method of claim 10 to adhere simultaneously to the respective surfaces of the aramid paper in the nip of a pair of rolls. The method of claim 10 , wherein the polymer of step c) comprises polyethylene terephthalate or a copolymer thereof. Aramid paper layer,
A first polymer layer,
At least one intermediate layer,
A method of forming a laminate comprising in order a second polymer layer and a second aramid paper layer,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
b) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
c) attaching the polymer to the more porous surface of the aramid paper obtained in step a),
d) attaching the polymer to the surface of the more porous side of the aramid paper obtained in step b), and e) laminating the aramid paper obtained in step c) and step d) with the intermediate layer. A method comprising. Aramid paper layer,
A first polymer layer,
At least one intermediate polymer layer;
A method of forming a laminate comprising in order a second polymer layer and a second aramid paper layer,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
b) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
c) a polymer layer having an intermediate layer interposed between the first and second polymer layers is attached to the respective porous surfaces of the aramid paper obtained in step a) and step b);
e) A method comprising laminating two sheets of paper and a polymer layer together. A method of forming a laminate comprising an aramid paper layer and a polymer layer in order,
a) Aramid paper is calendered between two rolls that differ in temperature by at least 20 ° C., where the surface of the paper exposed to the cold roll temperature is more porous than the opposite surface exposed to the hot roll temperature age,
b) A method comprising depositing a polymer on the more porous side surface of calendered aramid paper. The method of forming a laminate according to claim 14 , wherein the temperature of the two rolls differs by at least 50 ° C. The method of forming a laminate according to claim 14 , wherein the temperature of the two rolls differs by at least 100 ° C.   The polymer of step c) comprises polyethylene naphthalate, polybutylene terephthalate, polyetheretherketone, polyetherketoneketone, polyethersulfone, polyimide, polyetherimide, aromatic liquid crystalline polyester, mixtures or blends thereof. The method of claim 1. The polymer of step c) comprises polyethylene naphthalate, polybutylene terephthalate, polyetheretherketone, polyetherketoneketone, polyethersulfone, polyimide, polyetherimide, aromatic liquid crystalline polyester, mixtures or blends thereof. The method of claim 10 .